BMI Calculator
Table of contents
The BMI Calculator finds your Body Mass Index from height and weight and shows adult categories (underweight through obese) plus a healthy weight band. Choose metric or US units; your result updates instantly in the browser.
What is BMI?
Body Mass Index (BMI) is a simple calculation that uses your height and weight to estimate whether your weight is relatively low or high for your height.
It is widely used by doctors, nurses, and public-health programs as a quick screening tool. It does not measure body fat directly, but for many adults it is a practical starting point when discussing weight and health.
BMI formula
Metric (kg, m): BMI = weight (kg) ÷ height (m)² US customary: BMI = (weight in pounds ÷ height in inches²) × 703
BMI categories (adults)
For adults, common screening bands use the same cutoffs worldwide. Your result is compared to these ranges:
| BMI range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25 – 29.9 | Overweight |
| 30 and above | Obese |
Why use a BMI calculator?
- Instant screening against familiar categories
- Helps you notice gradual weight change over time
- Uses the same definition many clinicians reference in discussions
- Flags when follow-up with a professional may be useful
- Free, fast, and private when run in your browser like this one
Important: BMI limitations
BMI is useful, but it is not perfect. Think of it as a screening number, not a diagnosis.
It does not account for:
- Muscle mass — athletes may have a higher BMI with low body fat
- Where fat is stored on the body
- Age- or sex-related differences in body composition
- Bone density
What it means in plain language
A muscular person can have a BMI in the overweight range while carrying little body fat. That is why coaches and doctors often pair BMI with other measures when decisions matter.
What is a healthy BMI?
For most adults, a BMI between 18.5 and 24.9 is considered the normal or healthy range on standard charts.
Ideal health for you still depends on lifestyle, activity level, diet, sleep, stress, and medical history — so use BMI alongside professional advice, not instead of it.
- Lifestyle and habits
- Activity level
- Overall diet quality
- Personal and family medical history
Health risks by BMI range
Associations are statistical — your individual risk depends on many factors. These are common themes clinicians discuss when weight is far below or above the usual healthy band.
Underweight may be linked to nutritional deficiencies, weaker immunity, and bone health concerns.
Overweight is associated with higher rates of heart disease, high blood pressure, and joint loading over time.
Obesity is associated with higher risk of type 2 diabetes, stroke, and several cardiovascular conditions.
Always discuss personal risk with a qualified professional.
How to calculate BMI (step by step)
You do not need to crunch the math by hand — this page does it for you.
Pick your unit system, enter your height, then enter your weight. Your BMI, category, healthy weight band, and scale indicator appear immediately; there is no separate submit button because the tool updates live.
Who should use this calculator?
- Adults roughly 20 years and older looking for a quick screen
- Fitness enthusiasts tracking trends alongside other metrics
- Anyone monitoring weight loss or gain between checkups
When BMI is less reliable
- Children and teens — use growth charts and pediatric guidance
- Pregnancy — pregnancy weight goals differ; follow your care team
- Very muscular athletes — BMI may overestimate body fat risk
- Certain medical conditions that affect fluid or muscle mass
Tips to maintain a healthy BMI
- Eat a balanced diet rich in whole foods
- Exercise regularly with both cardio and strength work
- Track weight on a gentle schedule you can sustain
- Limit ultra-processed foods and sugary drinks
- Stay hydrated and prioritize consistent sleep
Frequently asked questions
What is a good BMI?
For most adults, a BMI between 18.5 and 24.9 falls in the normal or healthy range on standard charts. Your clinician may suggest a different target based on muscle mass, age, medications, and overall health.
Is BMI accurate?
BMI is accurate as a height-and-weight ratio, but it is only a rough indicator of body fat. It works best as a screening tool for typical adults and is less informative for athletes, some older adults, and certain ethnic groups where body composition differs.
Can BMI be wrong?
Yes. People with high muscle mass may have a high BMI without excess body fat. Someone within the normal BMI range can still have metabolic health issues. Always interpret BMI in context.
Should I worry about my BMI?
Use BMI as a starting point for conversation, not a verdict. If your number is outside the usual healthy band, or you have symptoms or risk factors, talk with a healthcare professional about next steps.